A corona charger has been used as a charging device for an electrostatic latent image carrier in a wide range of conventional electrophotographic image forming devices. The most common corona charger is of a scorotron type (hereinafter, “scorotron charger”) which is made up of a discharge electrode, an enclosure, and a grid electrode. The grid electrode, provided behind a discharge opening of the scorotron charger, is positioned to face the electrostatic latent image carrier, but so as to make no direct mechanical contact with the carrier. Ions are discharged at the surface of the electrostatic latent image carrier through the discharge opening to charge the surface of the electrostatic latent image carrier uniformly to a predetermined positive/negative potential. The discharge electrode in the scorotron charger is a sawtooth electrode, or an array of tungsten or needle-like wires each measuring 30 to 100 μm in diameter.
Other charging devices being in practical use include those of a roller charging scheme and a brush charging scheme. A roller is positioned, in the former, closely to or in contact with the electrostatic latent image carrier to apply voltage thereto; in the latter, a brush is brought into contact with the carrier for voltage application. These charging devices advantageously allow for relatively low voltage power supply, enabling large reduction in ozone production. For example, patent document 1 discloses a double-layered charge roller made of epichlorohydrin rubber. The technology reduces ozone production and also successfully addresses a problem of non-uniform charging in the roller charging scheme.
Patent document 1: Japanese Unexamined Patent Publication No. 5-341627/1993 (Tokukaihei 5-341627; published Dec. 24, 1993)